While the Financial District is not where you've asked about the Hotel Griffon might be what you are looking for in terms of ambiance and size. The service there is especially good.
http://www.hotelgriffon.com/
On the border of Nob Hill, Petite Auberge looks it the kind of place that could be awful but it's not. Service is excellent, and it's smaller with lovely furnishings .
http://www.jdvhotels.com/hotels/sanf...petite_auberge